As an example of a brake control device for a vehicle, a master cylinder device described in a Patent Literature 1 has been known. The master cylinder device according to the Patent Literature 1 pressurizes the operation fluid by a forward movement of a pressure piston in response to a braking operation by an operator of the vehicle. The pressurized operation fluid is supplied to a braking device (wheel brake cylinder) installed in each vehicle wheel thereby to apply each vehicle wheel with a braking force. A sealing member is disposed between the housing of the master cylinder body and the pressure piston for liquid-tightly sealed the housing and the pressure piston thereby.
Further, the master cylinder device of the Patent Literature 1 includes a mechanical type open/close valve and the plunger portion of the open/close valve is slidably fitted in a housing of the open/close valve at a base bottom portion. The master cylinder device supplies the master cylinder with a highly pressurized operation fluid via the open/close valve. Another sealing member is provided between the housing of the open/close valve and the base bottom portion of the plunger to liquid-tightly seal therebetween.